mAbs are successful biopharmaceuticals playing an important role in the treatment of cancer, autoimmunity and inflammatory diseases. Mammalian cells are the dominant system for the recombinant production of the biopharmaceuticals due to complex protein processing machinery for proper protein folding and assembly. Like other proteins, mAbs tend to form higher molecular weight aggregates during manufacturing, which negatively influence quality, safety and efficacy of the biotherapeutics. The protein aggregates can be removed during downstream processing, but this cost-intensive step leads to a reduction of process yields. An alternative to this expensive removal of HMW species during DSP represents the reduction of protein aggregates at its origin during upstream processing using bioprocess optimization. Such bioprocess optimization has been performed mainly to improve cell growth, product yield and glycosylation instead of decreasing protein aggregation of mAbs. One reason for this is the lack of analytical methods for the upstream characterization of mAb aggregation. In order to study protein aggregation upstream several methods were established for the characterization of soluble protein aggregates and large aggregate particles in cell culture samples. Using these novel methods cell culture conditions were screened for their influence on protein aggregation in cell cultures of Chinese hamster ovary (CHO) production cell lines. After identification of the most critical factors influencing protein aggregation, conditions were found for the reduction of aggregates in the cultures of the tested cell lines. Strikingly, the aggregate reducing conditions were validated in another cell culture medium and another CHO production cell line. Furthermore, it was revealed that leachables from cell culture vessels like Bisphenol A do not influence protein aggregation during bioprocessing, but can influence cellular performance of production cell lines. Moreover, this study revealed that the production enhancer VPA increased the specific productivity of mAbs produced in CHO, but also induced protein aggregation in a concentration dependent manner and negatively influenced the glycosylation pattern.
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Original Publication Date: 02/23/17